1. Field of Invention
This invention relates generally to heat exchangers and is particularly related to gas-to-gas heat recuperating apparatus. More specifically, the present invention relates to an air-to-air heat recuperating system comprising a plurality of stacked, spaced parallel flow channels uniquely designed and arranged to realize maximum heat transfer between flowing gas streams efficiently and economically.
2. The Prior Art
A variety of heat exchangers and heat recovery units have been available for years and some have been used in various industrial installations. Some of these heat exchangers are of the shell-and-tube variety where one fluid stream is passed through the shell and the other through tube, concurrently or countercurrently. Various design modifications such as the provision of finned tubes promotes turbulance and maximizes heat transfer between the two fluid streams.
Other heat recovery installations employ a heat exchanger system comprising a plurality of stacked tubes through which one of the fluid streams is passed while the other fluid stream flows across the tubes, usually at 90 degrees relative to the direction of fluid flow in the tubes. See, e.g., U.S. Pat. No. 2,296,570.
It is aximoatic, however, that in heat exchanger design, the desideratum is to maximize heat transfer efficiency of the unit while minimizing the cost of its utilization and operation in a particular installation. Additionally, while the shell-and-tube type heat exchangers are useful in some installations, there are other installations in which these exchangers cannot be conveniently integrated into the system, nor can they be used and operated efficiently and ecconomically. The use of heat exchangers comprising a plurality of stacked tubes offers a convenient alternative, and it is with this type of heat recovery unit that the present invention is particularly concerned.
Although some stacked tubes heat exchanger units have been designed and proposed by some of the prior art workers in this field, their poor heat transfer efficiency and high cost of operation has severely limited their practical industrial utilization. For example, the aforementioned U.S. Pat. No. 2,296,570 describes a cooling apparatus designed for a particular application (aeroplanes) and comprises a plurality of thin flat tubes through which so-called thin "strips" of compressed air flows from one end to the other end of the tubes, while cool air is passed across the surface of the tubes for cooling the compressed air flowing through the tubes.
In another more recent patent (U.S. Pat. No. 3,627,039), the heat exchanger comprises a plurality of pipes or tubes arranged axially parallel in several planes (stacks), one above or adjacent the other, and the respective ends of the tubes are combined to a common respective inlet and outlet apertures. The fluid medium to be cooled or heated enters through the inlet aperture, flows through the tubes and leaves through the outlet aperture, and the second fluid medium, which is used to cool or heat the fluid medium flowing through the tubes, is passed externally along the tubes laterally in a counterflow manner.
The prior art stacked, multiple tubes heat exchangers are usually expensive to operate due to their poor heat transfer efficiency and large pressure drop requirement. Their use, therefore, has been limited to particular systems where economic restrictions do not preclude their consideration. Economic demands in most systems, however, necessitate consideration and utilization of heat exchange units which exhibit superior heat transfer efficiency, lower pressure drop requirements and hence more economical operation. Thus, for numerous installations, there is still a need for a heat exchanger which can be conveniently integrated into the installation and used efficiently and more economically.